Directing heat-sensitive liquid form materials, such as dairy products, through an apparatus filled with steam, has been attempted using various devices. All known prior art apparatus have been plagued with the problem of burn-on. Burn-on occurs when heat-sensitive liquid form material touches a surface hotter than itself. In addition, burn-on builds up so rapidly on the heated interior surface of the apparatus that it flakes off and drops into the product itself.
Burn-on is particularly adverse to dairy products. When dairy products touch a surface warmer than itself, it acts on the proteins which will precipitate on to the warmer surface. As a layer of protein forms on the warmer surface, this layer also increases the thermal insulation formed by the wall with the cooler outside temperature. At the next cycling when steam reaches this layer of Protein covering the apparatus, a warmer surface temperature results. When the product comes back again, it comes over a warmer surface than before, more protein precipitates on the first layer than initially. This results in a rapid excessive build-up of burn-on. In addition to layers of protein precipitating on the warmer surface, the successive exposure to the top temperature on the steam denatures these layers and transforms them into what is called "burnt protein." This changes their color anywhere from light to dark brown with a characteristic unpleasant odor and taste which is then transferred to the product being processed.
In most prior devices, burn-on is also created by disadvantages in the design of the apparatus. It has been the common practice to expose the film of liquid form material directly to live steam at the very instant of the introduction of the film into the apparatus. Burn-on which occurs at this point cannot be prevented, resulting in operational problems due to the liquid form material film being broken down or interrupted. As the film is broken down or interrupted, splashing and additional burn-on results.
A second disadvantage in prior art devices is the creation of an "intermediate zone" where liquid form material and steam alternate resulting in additional burn-on. The heat-sensitive liquid form material is introduced in such a way that only a portion or fraction of the interior surfaces of the heated apparatus are covered with the liquid form material. This incomplete coverage of the heat-sensitive liquid form material on the internal surface of a heated apparatus always creates an intermediate zone. This alternating of a product and steam on the same surface is disastrous because each time the product progresses over the area just exposed to the steam, the product comes in contact with a surface warmer than itself. The repetition of alternating steam and liquid material over the same surface accelerates "burn-on" resulting in a rapid excessive buildup.
A further problem is caused by "hunting" which is attributed to the action of the control and level system. This "hunting" results from a variety of variables present, such as steam pressure, pumping, product viscosity, level control, etc. The level control alone varies because of its chain of action. The level change is sensed by the level sensors which transfer this information to the level transmitter which sends a signal to the level controller which sends the signal to another transmitter which finally acts on a flow control valve positioner or on a flow control pump. With this type of a flow control system, it is difficult to maintain a constant level since the margin of error of each instrument in the chain of level control adds to the delay in responding to changes of level.
In my co-pending application, Ser. No. 872,135 filed on 6/9/86 and entitled "Method and Apparatus for Sterilization of Liquids," an apparatus is described which utilizes both a film-forming gap to provide a film of liquid material down the inside surfaces of the vessel and a spray system which provides a shower of droplets between the interior wall vessel and the steam source. In the present application, an apparatus is described which eliminates the film-forming system and utilizes a spray system which provides both the film of liquid on the interior wall of the vessel, as well as a shower of droplets between the film and the steam system.